Background In October 2009, the French government organized a free, nationwide vaccination campaign against pandemic influenza A(H1N1), targeting pregnant women in particular. The aim of this analysis is to examine the factors associated with non-vaccination among pregnant women. Method Between October 12, 2009, and February 3, 2010, 882 pregnant women were randomly included in a prospective cohort study conducted in three Parisian maternity hospitals (the Coflupreg cohort). Results Among the 822 women included, 555 (62.9%) were not vaccinated by the time of delivery. The determinants associated with this non-vaccination were: geographic origin (Sub-Saharan Africa, adjusted odds ratio ORa=5.4 [2.3–12.7], North Africa, aaOR = 2.5 [1.3–4.7], and Asia, aaOR = 2.1 [1.7–2.6], compared to France and Europe) and socioeconomic status (artisans, merchants, and business owners, aaOR = 2.3 [2.0–2.6]; intermediate professions, ORa=1.3 [1.0–1.6], clerical and manual workers, ORa=2.5 [1.4–4.4] compared to managers and professionals). The probability of being vaccinated was higher among women who had been vaccinated against seasonal influenza in the previous five years (ORa=0.6 [0.4–0.8]) and among those who had quit smoking (ORa=0.6 [0.4–0.8]). Conclusion In this cohort, influenza A(H1N1) vaccination coverage was low, particularly among pregnant women of non-European foreign origin and among those belonging to less advantaged socio-professional categories. To improve their effectiveness, future vaccination campaigns could be tailored to these populations. (R.A.)